Ultrasonic doppler instrument

ABSTRACT

Medical ultrasonic doppler instrument in which transmitting and receiving transducers are mounted within a hollow casing on wavetransmission means of solid material cemented within one end of the casing and having planar surface means, preferably at an angle, to engage the skin of a living body being tested. Important features relate to the provision of wave absorpent material between the case and the wave-transmission means, the provision of a barrier between separate solid members to form the wave-transmission means, and the use of a biased amplifierdetector or a product detector.

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o EJHHWQ States 1 1 1 11 Flaherty et a1. 1 1 May 8, 1973 [54] ULTRASONICDOPPLER INSTRUMENT 3,208,286 9/1965 Richard .340 3 D [75] Inventors:John J. Flaherty, Elk Groove Vil- 332l959 5/1967 woofi eta!" la RichardM Soble both of 3,325,781 6/1967 Harris ..73/67.7X 1 n 3,383,678 5/1968Palmer ..340 1 chlcagol 3,427,866 2/1969 Weighart ..73/67.7 73 AssigneezMagnaflux Corporation, Chicagoy 3,430,625 3/1969 McLeod, Jr. ..73/194 XPrimary Examiner-Richard A. Farley [22] Flled: 1971 Attorney-Alberts,Brezina & Lund [21] Appl. No.: 126,336

[57] ABSTRACT Related U.S. Application Data Medical ultrasonic dopplerlnstrument in which trans- Commuano" of 658,117 3, 1967, mitting andreceiving transducers are mounted within abandoneda hollow casing onwave-transmission means of solid material cemented within one end of thecasing and [52] U.S. Cl ..340/1 R, 73/194 A, 128/205 F, having planarSurface means, preferably at an angle, to I l 340/3 D engage the skin ofa living body being tested Imporg f i 5 33 tant features relate to theprovision of wave absorpent 1 0 g 2 05 1 material between the case andthe wave-transmission l means, the provision of a barrier betweenseparate [56] R f Ct d solid members to form the wave-transmissionmeans, e erences l e and the use of a biased amplifier-detector or aproduct UNITED STATES PATENTS detector- 3,123,798 3/1964 Holloway et a1..340/3 14 Claims, 14 Drawing Figures 55 3(0 37 5 L S g o I I F PEE -AMPE X'QE DEMODULATOR P 52 T osc. 4o 39 31 M 1 AUDIO AUDlO u A 1, AMP. 912E'AMP.

EMITTEE FOLLOWEE ULTRASONIC DOPPLER INSTRUMENT This is a continuation ofSer. No. 658,117, filed Aug. 3, 1967 and now abandoned.

This invention relates to an ultrasonic instrument and more particularlyto an ultrasonic instrument which uses the well-known Doppler principleto detect and measure motion of reflecting surfaces within a body.Although having other applications, the instrument is specificallydesigned and particularly advantageous in medical applications, whereinthe body is that of a human or another animal. By way of example, theinstrument is usable in the measurement of the velocity of flow of bloodand in the detection of movement of organs such as the heart. It candetect a fetal heartbeat at a very early stage in the development of theembryo.

In accordance with the Doppler principle, the frequency of a receivedwave is shifted relative to its frequency during transmission when thereis relative movement of the transmitting and receiving points toward oraway from each other, the frequency being increased with thetransmitting and receiving points are moved closer to each other andbeing decreased when the points are moved away from each other. Thefrequency shift is proportional to the velocity of the relative movementand is also proportional to the fixed frequency of the transmitted wave,while being inversely proportional to the velocity of propagation of thewave through the medium between the transmitting and receiving points.By the same principle, a wave transmitted from a transmitting point to areflecting surface and thence to a receiving point will be shifted infrequency during travel between the transmitting point and thereflecting surface and again during travel between the reflectingsurface and the receiving point if there is relative movement betweenthe reflecting surface and the transmitting and receiving points, therelative position of which may be fixed.

Ultrasonic instruments have heretofore been proposed which transmitultrasonic energy into a body and receive reflected energy which isfrequency-shifted due to movement of a reflecting surface within thebody, according to the Doppler principle. Such instruments, however,have had limited sensitivity and accuracy, have been erratic inoperation and the indications produced have been such that it has beenquite difficult to obtain a reliable diagnosis.

The present invention was evolved with the general object of overcomingthe disadvantages of prior art instruments and of providing ultrasonicinstruments which are highly sensitive and accurate and being veryreliable and trouble-free in operation.

In accordance with this invention, an ultrasonic instrument is providedwhich includes a transmitting transducer for transmitting ultrasonicenergy into a body to produce reflected energy including frequencycomponents at the transmission frequency correspond ing to reflectionsfrom stationary interfaces and frequency-shifted componentscorresponding to reflections from moving interfaces, receivingtransducer means being provided for receiving the reflected energy toproduce a corresponding electrical signal. The signal is amplified andapplied to detector means functioning to produce an output signal inresponse to frequency-shifted components of the amplified electricalsignal. The instrument further includes means for minimizing the effectof components at the transmission frequency to obtain maximumsensitivity to the frequency-shifted components. This feature is veryimportant, because it has been found that the limitations in accuracyand sensitivity of prior instruments, and also the erratic operationthereof arise to a large extent from the effect of components at thetransmission frequency.

In accordance with a specific feature of the invention, a gain controlmeans is associated with the amplifier means used to apply the receivedsignal to the detector, the gain of the amplifier means being therebyadjustable to permit maximum amplification of frequency-shiftedcomponents without overloading by components at the transmissionfrequency. This feature is quite important because it is found that theam plitude of the component at the transmission frequency is unavoidablysubject to wide variations, dependent upon the number and character ofstationary reflecting surfaces within the body. By adjustment of thegain to obtain maximum response to the frequency-shifted componentswithout overloading by the components at the transmission frequency, thesensitivity, accuracy and reliability of the instrument is greatlyincreased.

Another important feature of the invention is in the provision ofimproved demodulation means operable over a wide dynamic range tofurther minimize the effect of components at the transmission frequencyand to otherwise obtain maximum sensitivity to the frequency-shiftedcomponents. In one preferred embodiment of the instrument, agroundedemitter detector or any equivalent type of detector is used, toobtain an increased dynamic range and to also provide amplification withincreased sensitivity. In another preferred embodiment, a productdetector is used to obtain a very high dynamic range and to furtherimprove performance. A further important feature of the invention is inthe mounting of the transmitting and receiving transducers in a probeunit with an acoustic barrier between the transducers so as to permitthe transducers to be located in close proximity while minimizing directcoupling of the transmitted signal into the receiving transducer. Thisfeature further improves the sensitivity and reliability of theinstrument.

Another important feature of the invention relates to the provision ofmeans for maintaining a constant acute angle of transmission of theenergy into the body. With this feature, the effect of components at thetransmitted frequency, produced by stationary interfaces, is minimized,and in addition, the accuracy of measurement is increased, particularlywith regard to measurement of flow as, for example, the flow of blood.With a constant angle, it is possible to accurately determine the flowrate. An additional advantage is that the ease of operation oftheinstrument is increased.

A further feature of the invention relates to the provision of means forindicating the magnitude of the frequency shift, to thereby provide anindication of velocity. This feature is particularly important incombination with the constant angle of transmission feature.

Additional important features of the invention relate to the provisionof a pair of spaced receiving transducers which develop a pair ofreceived signals, such being preferably applied in opposition to eachother to balance out components at the transmission frequency.

An important advantage is that the frequency deviation is doubledwithout doubling the transmission frequency, and in addition the totalreceived energy is doubled.

In one embodiment, a transmitting transducer is positioned between thepair of receiving transducers while in another embodiment the receivingtransducers are used also as transmitting transducers. The receivingtransducers, and the transmitting transducer may preferably be formed byproviding spaced electrodes on a single plate of piezoelectric material.

This invention contemplates other objects, features and advantages,which will become more fully apparent from the following detaileddescription taken in conjunction with the accompanying drawings whichillustrate preferred embodiments and in which:

FIG. 1 is a perspective view of an ultrasonic instrument constructedaccording to the principles of this invention, in use in detecting theflow of blood in a patient;

FIG. 2 is a schematic block diagram of the electrical circuitry of theultrasonic instrument of FIG. I;

FIG. 3 is a circuit diagram showing amplifier, demodulator and band passfilter circuits of the system of FIG. 2;

FIG. 4 is a cross-sectional view of a probe unit of the instrument ofFIG. 1;

FIG. 5 is a cross-sectional view taken substantially along line VV ofFIG. 4;

FIG. 6 is another cross-sectional view taken substantially along lineVI-VI of FIG. 4;

FIG. 7 is a side elevational view of an end portion of a modified probeunit constructed according to the principles of this invention;

FIG. 8 is a cross-sectional view taken substantially along lineVIII-VIII of FIG. 7;

FIG. 9 is a schematic block and circuit diagram illustrating a modifiedform of demodulator circuit, according to the principles of theinvention;

FIG. 10 is a cross-sectional view of a modified probe unit;

FIG. II is a cross-sectional view taken substantially along line XI-XIof FIG. 10;

FIG. 12 is a schematic diagram illustrating the connection of the probeunit of FIGS. 10 and 11 to electrical circuitry; and

FIGS. I3 and 14 are schematic diagrams illustrating modified connectionsof the probe unit of FIGS. 10 and I1 to electrical circuitry.

Reference numeral It) generally designates an ultrasonic instrumentconstructed according to the principles of this invention. In general,the instrument 10 comprises a probe unit II which is connected by meansof a cable I2, having two shielded lines I3 and I4 therein, to aportable indicating and energizing unit I6. The unit I6 has input jacksI7 and 18 for receiving plugs connected to the lines I3 and I4 andfurther includes a speaker I9, control knobs 21 and 22 and a filterswitch 23.

In the operation of the instrument I0, the probe 11 is placed againstthe body to be examined. As shown in FIG. I, the probe unit II is placedagainst the neck of a patient 26 to transmit ultrasonic energy into andalong an artery in the neck, with frequency-shifted energy beingreceived back by the probe I1, reflected from moving blood in theartery. The instrument operates to produce a characteristic whishingsound in the speaker 19 in response to the flowing blood. In addition,throbbing sounds are produced in response to pulsations in the bloodvessels, or from other moving interfaces within the body. It will beunderstood that although the instrument is specifically designed formedical use, it is not necessarily limited thereto, and it may be usedin testing any desired body such as, for example, a pipe in which theliquid or gas is flowing, or any body having vibrating or movinginterfaces.

The control knob 22 controls an on-off switch and the sensitivity of theinstrument and permits the attainment of optimum performance, asdescribed hereinafter. The switch 23 controls the filter to obtainoptimum attenuation of noise signals. A built-in battery charger andmeter scale are provided to insure a proper electrical supply for theinstrument.

The unit 16 is small and compact and includes a lightweight case 27having a lid 28 and a handle 29 for easy portability. The instrument canbe used in many different applications ranging from those which resemblethe functions of an ordinary stethoscope to such applications asmeasuring the speed ofblood flow in veins and arteries, early detectionof fetus and localization of placenta in pregnancies and qualitativeblood flow determinations in carotid and vertebral arteries, by way ofexample.

FIG. 2 is a schematic block diagram of the electrical circuitry of theinstrument 10. A transmitting transducer 31 located in the probe 11, isconnected through the shielded line 13 to an RF oscillator 32 fortransmitting continuous ultrasonic energy into the patients body. Afrequency of five megacycles may be used, for example. A receivingtransducer 33, also located in the probe 11, is connected through theshielded line 14 to the input of a preamplifier 34 having an outputapplied through a sensitivity control device 35 to a tuned amplifier 36which supplies an amplified signal to a demodulator 37. The amplifiedsignal applied to the demodulator 37 includes frequency components atthe transmission frequency corresponding to reflections from stationaryinterfaces and also contains frequencyshifted components correspondingto reflections from moving interfaces. The demodulator 37 responds tosuch components to produce an output signal having a frequency equal tothe difference in the frequencies of such components, normally in theaudio frequency range.

The output of the demodulator 37 is applied through a band pass filter38, which functions to remove higher frequency components, to the inputof an audio preamplifier 39, the output of the preamplifier 39 beingapplied to the input of an audio amplifier 40. One output of the audioamplifier 40 is applied to a selector switch 41, which functions toselectively apply the audio signal either to the speaker I9, or toearphones 452. A second output of the audio amplifier 40 is appliedthrough an emitter-follower stage 43 to be applied to a frequency meter44 and/or a recorder 45.

With proper adjustment of the sensitivity control device 35, a highsensitivity to the received frequencyshifted signal is obtained toproduce a maximum output under all conditions of operation, as will beclarified from a consideration of the circuit diagram of FIG. 3,

which shows the circuits of the preamplifier 34, the sensitivity controldevice 35, the tuned amplifier 36, the demodulator 37 and the band passfilter 38.

Referring to FIG. 3, the receiving transducer 33 is connected to theprimary winding 47 of a transformer 48 having a secondary winding 49.One terminal of the secondary winding 49 is connected to ground and theother terminal is connected through a coupling capacitor 51 to the baseof a transistor 52 which is connected through a resistor 53 to groundand through a resistor 54 to a line 55 which is connected through afilter capacitor 56 to ground and through a decoupling resistor 57 to aline 58. Line 58 is connected to ground through another filter capacitor59 and is connected through a resistor 60 to a line 61 to which a supplyvoltage is applied. In particular, the line 61 is connected through anon-off switch 62 to a battery 63, and is also connected through anadjustable resistor 64, a Zener diode 66 and a meter 67 to ground. Thediode 66 regulates the voltage on the line 61, which may be adjusted byadjustment of the resistor 64. The meter 67 measures the current flowthrough the diode 66 and thereby provides an indication of the conditionof charge of the battery 63. A battery charger 68 is connected to thebattery 63 and to a power supply input 69, to charge the battery 68 whenconvenient.

The pre-amplifier transistor 52 has an emitter connected to groundthrough a resistor 71 and a capacitor 72 in parallel and has a collectorconnected through a potentiometer 73 to the line 55. The potentiometer73 forms the sensitivity control device 35 and has a movable contactconnected to the control knob 22.

I The movable contact of the potentiometer 73 is connected through acoupling capacitor 75 to a circuit point 76 which is connected through aresistor 77 to ground and through a resistor 78 to the line 58. Circuitpoint 76 is also connected through a resistor 80 to the base of atransistor 82 having an emitter connected to ground through a capacitor83 and a resistor 84 and having a collector connected to the line 58through an adjustable inductor 86. The collector of the transistor 82 isalso connected through a capacitor 87 to ground and through a capacitor88 to the base of a transistor 89 in the demodulator stage 37. Thetransistor 82 and associated circuit elements form the tuned amplifier36, the inductor 86 being adjustable to tune the stage to passfrequencies in a range including the frequency of the transmitted energyand the frequencies of frequency-shifted components.

The base of the diode 89 in the demodulator circuit 37 is connected tothe movable contact of a potentiometer 91 which is connected betweenground and the line 58 while the emitter of the transistor 89 isconnected through a resistor 92 to ground. The collector of thetransistor 89 is connected through a resistor 93 to the line 58, througha capacitor 94 to ground and through an inductor 96 to a circuit point97 which is connected through a capacitor 98 to ground. The capacitors94 and 98 together with the inductor 96 form a filter for removingcomponents in the range of the transmitted frequency.

In the operation of the circuit as thus far described, the potentiometer91 is adjusted to so bias the transistor 89 as to cause conduction ofthe transistor 89 only during positive half-cycles of the signal appliedthrough the coupling capacitor 88 from the collector of the band passamplifier transistor 82. Negative-going signals are thus developed atthe collector of the demodulator transistor 89 having an amplitude whichvaries at a beat frequency range, equal to the difference between thefrequency of a frequency-shifted component and the transmittedfrequency. The signal developed at the collector of the transistor 89also contains frequency components in the range of the transmittedfrequency, such frequency components being removed by the filter circuitincluding capacitors 94 and 98 and the inductor 96.

The adjustability of the operation of the circuit is important,particularly with respect to the sensitivity control potentiometer 73which permits adjustment of the amplification such that thefrequency-shifted components are amplified to a maximum extent withoutoverloading of the amplifier circuit. In this connection, it is notedthat the overall amplitude of the received signal is subject to widevariations. For example, the component at the transmitted frequency maybecome quite large when there is a stationary reflecting surface ofsubstantial area in the path of the transmitted energy. The adjustmentof the inductor 86 is also important in obtaining amplification of thefrequency-shifted components and the adjustability of the potentiometer91 is important to insure optimum operation of the demodulator circuit.

It is important to note that the demodulator circuit as illustratedprovides both demodulation and amplification and with properadjustments, it operates over a wide dynamic range.

The signal developed at the circuit point 97 is applied through aresistor 99 to a circuit point 101 which is connected through acapacitor 103 to a circuit point 104 connected to ground through aswitch 106 and also connected through a capacitor 107 to a circuit point108 which is connected through a capacitor 109 to ground and through aresistor 111 to the circuit point 101. This arrangement provides afilter circuit for attenuating higher frequency components of the signaldeveloped at the circuit point 97, maximum filtering being obtained withthe switch 106 closed.

The circuit point 108 is connected through a capacitor 112 to the baseof a transistor 113 and also to the moveable contact of a potentiometer114 connected between ground and the line 61. The emitter of thetransistor 1 13 is connected to ground through a capacitor 115 and aresistor 116 while the collector thereof is connected through apotentiometer 117 to the line 61. The movable contact of potentiometer117 is connected through a coupling capacitor 118 to a line 119, line119 being connected to the input of the audio amplifier 40. Thepotentiometer 117 forms an audio volume control.

The pitch of the sound produced in the speaker 19, or in the earphones42, varies with the speed of the moving interfaces relative to the lineof transmission of the ultrasonic energy and the corresponding frequencyof the beats produced by the reflected energy. When the instrument 10 isused to detect blood flow in an artery, for example, a periodic lowthumping sound corresponding to the rapid expansion of the artery wallat each heartbeat is heard with the transducer placed to transmit energyalong a line normal to the arterial axis.

in this position, no Doppler frequency shift due to the moving bloodoccurs, since the blood movement is transverse to the transmission axisand there is no component of motion in the transmission direction. Asthe transducer is tilted off normal, however, so that a component of themotion of the blood in the artery is along the transmission axis, aperiodic higher frequency swishing sound is heard corresponding to themovement of blood in the artery. The intensity of the swishing soundincreases with the heartbeats which force blood through the artery at arapid rate. The sound decreases in intensity and frequency during theperiodic pauses between heartbeats. The pitch of the sound depends uponthe speed flow of the blood in the blood vessel, the angle of thetransmission axis relative to the axis of the blood vessel, and thefrequency of the transmitted energy. Thus for a given frequency oftransmission and a given angle of transmission relative to the axis ofthe blood vessel, the pitch of the sound emitted from the speaker 19varies proportionately with the velocity of the blood in the arterybeing observed. If the frequency and the angle of transmission areknown, an accurate determination of the blood velocity may be made. Thismay be accomplished accurately by means of the frequency meter 44, or byanalysis of the record produced by the recorder 45. 124

The physical construction of the probe 11 is illustrated in FIGS. 46. Acylindrical case 121 is provided which may preferably of an epoxymaterial having a length of about 2.75 inches and an inner diameter ofabout 0.625 inches. A transducer assembly 122 is affixed inside one endof the case 121, preferably by means of an epoxy cement. The assembly122 comprises two wave-transmitting members 123 and 124 each having agenerally semi-cylindrical shape, with outwardly projecting shoulders125 and 126 at the outer ends thereof, engageable with the insidesurface of the casing 121. A solid rectangular barrier layer 128 isdisposed between the wave-transmission members 123 and 124 to minimizedirect transmission of energy therebetween. An annular layer 129 isdisposed around the assembly, between the outer cylindrical surfaces ofthe members 123 and 124 and the internal cylindrical surface of thecasing 121. The members 123 and 124 are preferably of a material havinga very low attenuation of acoustic waves, while the layer 128 and thelayer 29 are preferably of a material having very high attenuationcharacteristic. By way of example, the layers 128 and 129 may be formedof a material which is of a mixture of 80% Tungsten and bakelite epoxy.

The outer faces of the wave-transmission members 123 and 124 arepreferably flush with the end of the casing 121, in a plane transverseto the axis of the easing 121. The transmitting transducer 31 and thereceiving transducer 33 are secured against opposite faces 131 and 132of the wave-transmission members 123 and 124. The faces 131 and 132 areat slight angles, preferably on the order of 2, with respect to a planetransverse to the axis of the casing 121, for converging the axes oftransmission and reception of the ultrasonic energy.

To minimize electrical coupling between the transmitting and receivingtransducers and the lines connected thereto, a tube 134 is supportedcoaxially within the casing 121. Lead wires 135 and 136, connected toelectrodes on the back and front surfaces of the transmitting transducer31 and lead wires 137 and 138, connected to electrodes of the receivingtransducer 33, are taped to the tube 134. Inner conductors 139 and 140of the shielded lines 13 and 14 are connected to the wires 135 and 137,while the shields 141 and 142 of the lines 13 and 14 are connected tothe wires 136 and 138. The

connections are preferably made by soldering, with tape 144 being usedto hold the wires in place during soldering, an outer layer of tape 145being applied after the connections are completed. A conetic shield 147is disposed inside the tube 134 after the connections are made, theshield 147 being in the form of foil rolled into a tube. An annularmember 149 is provided for supporting the tube 134 and has openings forpassage of the lines 13 and 14 therethrough. The end portion of thecasing 121 is filled with a suitable potting compound 150, and a slopingconical strain relief mold 151 is provided on the end of the casing 121,for support of the cable 12 containing the shielded lines 13 and 14.

With this arrangement, there is minimum electrical coupling between thetransducers 31 and 33 and the lines leading thereto and through thebarrier layer 128, there is minimum acoustic coupling. These featuresare important in achieving maximum sensitivity to the shifted componentsof the received signals.

FIGS. 7 and 8 illustrate a modified probe construction. In thisarrangement, a transducer assembly 156 is provided which includes a pairof wavetransmission members 157 and 158 similar to the members 123 and124, but of greater length to project from the end of the casing 121.The members 157 and 158 have end faces 159 and 160 in a plane which isat an acute angle relative to a plane transverse to the axis of thecasing 121v Preferably the angle is on the order of from 20 to 40degrees and most preferably it is approximately 30 degrees as shown.With this arrangement, the energy is transmitted into the body at anacute angle to the sur face of the body, the angle with respect to thesurface of the body being on the order of from 40 to 80 and mostpreferably being approximately 60 with the illustrated arrangement. Abarrier layer 161, similar to the layer 128, is disposed between themembers 157 and 158 and an outer layer 163 is provided similar to thelayer 129. The transducers 31 and 33 in this arrangement are cemented toopposite end faces 165 and 166 of the members 157 and 158, the faces 165and 166 being preferably at a slight angle which in this arrangement maybe somewhat less than 2 degrees.

With this arrangement, optimum measurement of the velocity of flow ofblood in a patients body can be obtained. The energy is transmitted andreceived along a path which is at an angle sufficiently great to obtaina measurable component of velocity but less than that at which theefficiency of transmission of the waves into the body and out of thebody becomes reduced. The faces 159 and 160 can be placed flat againstthe surface of the body without requiring any great amount ofmanipulation to obtain the desired response. The arrangement is furtheradvantageous in that a constant angle of transmission is provided, topermit accurate measurement of the velocity of the blood flow.

FIG. 9 illustrates a modified circuit arrangement wherein a productdetector circuit 171 is substituted for the demodulator circuit 37. Theproduct detector circuit 71 comprises a field effect tetrode 172 havingone terminal connected to ground, one control terminal connected througha diode 173 to an output front the RF oscillator circuit 32 and anothercontrol terminal connected through a resistor 174 to ground and througha capacitor 176 to the output of the tuned amplifier 36, and an outputterminal connected through a resistor 177 to a line 178, through acapacitor 179 to ground and through an inductor 181 to a circuit point182. The circuit point 182 is connected through a capacitor 183 toground and through a coupling capacitor 184 to a line 186 which may beconnected to the input of the audio amplifier 40 or to the input of thepre-amplifier 39. Line 178 is connected to a power supply terminal 187,to which minus 12 volts may be applied, for example, and line 178 isalso connected through a filter capacitor 188 to ground.

With the product detector 171, an amplified reflection signal containingfrequency-shifted components from moving interfaces within the bodybeing tested is taken from the tuned amplifier 36 and applied to onecontrol terminal of the field effect tetrode 172. A signal having thefrequency of the transmitted signal is taken from the RF oscillator andapplied to the other control terminal of the tetrode 172, which causesthe tetrode 172 to act as a gate allowing passage of the reflectedsignal only during certain portions of the oscillator signal, andproducing a low frequency signal having a frequency equal to thedifference in frequency between the transmitted signal and the reflectedsignal. High frequency components are filtered from the gated signal bythe capacitors 179 and 183 operating in conjunction with the inductor181.

The product detector operates over an extremely wide dynamic range,minimizing the effect of the signal at the transmitted frequency, andincreasing the sensitivity to the frequency-shifted components.

Referring now to FIGS. and 11, reference numeral 190 generallydesignates a modified probe unit which includes a relatively long andnarrow rectangular plate 191 of quartz or other piezoelectric materialwith an electrode 192 covering substantially the entire lower face ofthe plate 191 and with three electrodes 193, 194 and 195 in spacedrelation along the upper face of the plate 191. The electrode 192 on thelower face of the plate 191 may be directly coupled to the surface of abody to be tested or, as shown, may be cemented to the upper face ofasupport and coupling plate 196 hav ing a lower face engageable with thesurface of the body to be tested. The plate 196 is supported within theend ofa suitable housing 197.

To provide electrical connections to the electrodes, a wire 198 isconnected at one end to the electrode 192 and at its opposite ends to apair of wires 199 and 200 respectively connected to shield conductorsofa pair of cables 201 and 202. A wire 203 is connected between theelectrode 1941 and a wire 204 of the cable 201 while wires 205 and 206are connected between electrodes 193 and 195 and wires 207 and 208 ofthe cable 202. The wire connections are secured to a support tube 209 bysuitable tape 210 and the support tube 209 as well as the cables 201 and202 are supported by a support member 21 1 within the housing 197.

With this arrangement, three effectively separate transducers areprovided in spaced relation, although a single plate of piezoelectricmaterial is used. It will be appreciated, of course, that threecompletely separate transducers might be used, if desired.

Referring now to FIG. 12, the center electrode 194 is connected to oneoutput terminal 213 of an oscillator 214 having a second terminal 215connected to ground and to the electrode 192. Thus the portion of theplate 191 between the electrodes 192 and 194 act as a transmittingtransducer. The electrodes 193 and are connected to opposite endterminals of a primary winding 216 of a coupling transformer 217 havinga secondary winding 218 connected to input terminals of a preamplifier219. A center tap of the primary winding 216 is connected to ground. Theoutput of the pre-amplifier 219 may be connected through the sensitivitycontrol device 35 to the the same circuit arrangement described above inconnection with FIG. 2, including the tuned amplifier 36, thedemodulator 37, the band pass filter 38, the audio prei-amplifier 39,the audio amplifier 40, the selector switch 41, the speaker 19 and thehead phones 42.

In operation, the portions of the plate 191 between the electrodes 193and 195 and the electrode 192 function as a pair of receivingtransducers. With the receiving transducers being spaced along a linegenerally parallel to the direction of blood flow, there will be apositive Doppler frequency shift in the signal developed by onetransducer while there will be a negative Doppler frequency shift in thesignal produced by the other receiving transducer. This results in animportant advantage in that when the outputs from the two transducersare arithmetically subtracted, the resulting frequency shift is twicethat produced by one transducer alone. Thus the frequency deviation isdoubled without doubling the transmitted frequency. As a result, it ispossible to use a lower transmitted frequency and to obtain increaseddepth of penetration, while increasing sensitivity.

Another important advantage of the arrangement is that the coupling fromthe transmitting transducers to the receiving transducers is equal andsince the outputs are arithmetically subtracted, the energy at thetransmitted frequency may be effectively cancelled out.

Another advantage is that the total received energy is doubled, sincethe total receiver crystal area is doubled.

Still another advantage of the arrangement is that the maximum output isobtained from a comparatively narrow region centered on a plane midwaybetween the receiving transducers. With this feature, the generation ofextraneous indications is minimized, and it is possible to localize theregion under inspection, to greatly increase the diagnostic potential ofthe system.

A still further advantage of the arrangement is in the simplifiedtransducer construction, using a common plate of piezoelectric material.

Referring now to FIG. 13, a modified circuit arrangement is shown inwhich the portions of the plate 191 between the electrodes 193 and 195are used as transmitting transducers as well as receiving transducers.In this arrangement, the electrodes 193 and 195 are coupled throughvariable inductors 221 and 222 to the output terminal 213 of theoscillator 214 and are also coupled directly to input terminals of thepre-amplifier 219. With this arrangement, a bridge circuit is formed inwhich the signal at the transmitted frequency is balanced out, while thepositive and negative Dopplershifted received signals are applied inopposition to develop a doubled frequency deviation.

FIG. 14 illustrates another modification in which the electrodes 193 and195 are connected to the RF oscillator 214 through primary windings 223and 224 of transformers 225 and 226 having secondary windings 227 and228 which are differentially connected to input terminals of thepre-amplifier 219. Here again, the signals at the transmitted frequencyare balanced out while the positive and negative Doppler-shifted signalsare combined to produce a double frequency deviation. It will beappreciated that in both of the modifications shown in FIGS. 13 and 14,the center electrode 194 is not utilized and it may be eliminatedentirely, if desired. Here again, two completely separate transducersmay be used, if desired.

It will be understood that modifications and variations may be effectedwithout departing from the spirit and scope of the novel concepts ofthis invention.

We claim as our invention:

1. In a medical ultrasonic doppler instrument, transmitting transducermeans for transmitting ultrasonic energy at a transmission frequencyinto a living body to produce reflected energy including frequencycomponents at said transmission frequency corresponding to reflectionsfrom stationary interfaces within said living body and frequency-shiftedcomponents corresponding to reflections from moving interfaces withinsaid living body, receiving transducer means for receiving saidreflected energy to produce a corresponding electrical signal, amplifiermeans for amplifying said electrical signal, deflector means responsiveto the amplified electrical signal to produce an output signal inresponse to frequency-shifted components of said electrical signal,hollow casing means having an open end, wave-transmission means of solidmaterial having a low ultrasonic wave attenuation characteristic anddisposed at said open end of said hollow casing, sealing means defininga sealed connection between said wave-transmission means and said hollowcasing means, said wave-transmission means having planar surface meansarranged to engage the skin of said living body and having first andsecond surface portions opposite said planar surface means and facingthe interior of said hollow casing, said transmitting and receivingtransducer means respectively comprising transmitting and receivingtransducers disposed within said housing and respectively securedagainst said first and second surface portions for propagation of wavesfrom said transmitting transducer through said wave-transmission meansinto the living body and for propagation of reflected energy backthrough said wave-transmission means to said receiving transducer.

2. In a medical ultrasonic doppler instrument as defined in claim I,energization means for energizing said transmitting transducer, andelectrical connection means for connection of said transmitting andreceiving transducers to said energization and amplifier means.

3. In a medical ultrasonic doppler instrument as defined in claim 2,said sealing means being effective to prevent entry of fluids into theinterior of said hollow casing means to protect said electricalconnection means.

41. In a medical ultrasonic doppler instrument as defined in claim 1,said wave-transmission means having outwardly projecting shoulder meansfitted in said open end of said casing means, said sealing means beingdisposed between said shoulder means and an inside surface portion ofsaid hollow casing means, and a barrier layer of wave-absorbent materialdisposed between the inside surface of said casing and the portion ofsaid wave-transmission means inside said shoulder means.

5. In a medical ultrasonic doppler instrument as defined in claim 1, alayer of a solid wave-attenuating and impervious material forming abarrier, said wavetransmission means comprising first and second solidmembers on opposite sides of said barrier and having end surfaces withinsaid casing defining said first and second surface portions, said firstand second members and said barrier having co-planar surfaces definingsaid planar surface means.

6. In a medical ultrasonic doppler instrument as defined in claim 5,said hollow casing means having an end surface co-planar with saidco-planar surfaces of said first and second members and said solidbarrier.

7. In a medical ultrasonic doppler instrument as defined in claim ll,said first and second surface portions being inclined at substantiallyequal angles relative to a central plane transverse to said planarsurface means to effect transmission and reception along paths havingaxes intersecting at a point within said living body.

8. In a medical ultrasonic doppler instrument as defined in claim 1,said planar surface means being inclined at an angle relative to a planethrough the axes of transmission of ultrasonic energy from and to saidtransmitting and receiving transducers so as to transmit and receiveenergy along a direction at a fixed acute angle relative to the surfaceof the living body.

9. In a medical ultrasonic doppler instrument as defined in claim 8,said fixed acute angle being on the order of from 40 to 10. In a medicalultrasonic doppler instrument as defined in claim 1, said detector meansincluding an amplifier device having first, second and third electrodeswith the effective impedance between said second and third electrodesbeing controlled by the signal applied between said first and secondelectrodes, a power supply meansincluding a load impedance connectingsaid second and third electrodes to said power supply, means forapplying said amplified electrical signal between said first and secondelectrodes, and adjustable bias means for biasing said first electroderelative to said second electrode.

11. In a medical ultrasonic doppler instrument as defined in claim 10said amplifier device being a transistor having base, emitter andcollector electrodes respectively constituting said first, second andthird electrodes.

12. In a medical ultrasonic doppler instrument as defined in claim 11,said adjustable bias means comprising a potentiometer having endterminals coupled to said power supply and having a movable contactcoupled to said base electrode.

field effect device having a pair of control electrodes, means forapplying said amplified electrical signal to one of said electrodes, andmeans for applying said signal from said oscillator to the other of saidelectrodes.

1. In a medical ultrasonic doppler instrument, transmitting transducermeans for transmitting ultrasonic energy at a transmission frequencyinto a living body to produce reflected energy including frequencycomponents at said transmission frequency corresponding to reflectionsfrom stationary interfaces within said living body and frequency-shiftedcomponents corresponding to reflections from moving interfaces withinsaid living body, receiving transducer means for receiving saidreflected energy to produce a corresponding electrical signal, amplifiermeans for amplifying said electrical signal, detector means responsiveto the amplified electrical signal to produce an output signal inresponse to frequency-shifted components of said electrical signal,hollow casing means having an open end, wavetransmission means of solidmaterial having a low ultrasonic wave attenuation characteristic anddisposed at said open end of said hollow casing, sealing means defininga sealed connection between said wave-transmission means and said hollowcasing means, said wave-transmission means having planar surface meansarranged to engage the skin of said living body and having first andsecond surface portions opposite said planar surface means and facingthe interior of said hollow casing, said transmitting and receivingtransducer means respectively comprising transmitting and receivingtransducers disposed within said housing and respectively securedagainst said first and second surface portions for propagation of wavesfrom said transmitting transducer through said wave-transmission meansinto the living body and for propagation of reflected energy backthrough said wave-transmission means to said receiving transducer.
 2. Ina medical ultrasonic doppler instrument as defined in claim 1,energization means for energizing said transmitting transducer, andelectrical connection means for connection of said transmitting andreceiving transducers to said energization and amplifier means.
 3. In amedical ultrasonic doppler instrument as defined in claim 2, saidsealing means being effective to prevent entry of fluids into theinterior of said hollow casing means to protect said electricalconnection means.
 4. In a medical ultrasonic doppler instrument asdefined in claim 1, said wave-transmission means having outwardlyprojecting shoulder means fitted in said open end of said casing means,said sealing means being disposed between said shoulder means and aninside surface portion of said hollow casing means, and a barrier layerof wave-absorbent material disposed between the inside surface of saidcasing and the portion of said wave-transmission means inside saidshoulder means.
 5. In a medical ultrasonic doppler instrument as definedin claim 1, a layer of a solid wave-attenuating and impervious materialforming a barrier, said wave-transmission means comprising first andsecond solid members on opposite sides of said barrier and having endsurfaces within said casing defining said first and second surfaceportions, said first and second members and said barrier havingco-planar surfaces defining said planar surface means.
 6. In a medicalultrasonic doppler instrument as defined in claim 5, said hollow casingmeans having an end surface co-planar with said co-planar surfaces ofsaid first and second members and said solid barrier.
 7. In a medicalultrasonic doppler instrument as defined in claim 1, said first andsecond surface portions being inclined at substantially equal anglesrelative to a central plane transverse to said planar surface means toeffect transmission and reception along paths having axes intersectingat a point within said living body.
 8. In a medical ultrasonic dopplerinstrument as defined in clAim 1, said planar surface means beinginclined at an angle relative to a plane through the axes oftransmission of ultrasonic energy from and to said transmitting andreceiving transducers so as to transmit and receive energy along adirection at a fixed acute angle relative to the surface of the livingbody.
 9. In a medical ultrasonic doppler instrument as defined in claim8, said fixed acute angle being on the order of from 40* to 80*.
 10. Ina medical ultrasonic doppler instrument as defined in claim 1, saiddetector means including an amplifier device having first, second andthird electrodes with the effective impedance between said second andthird electrodes being controlled by the signal applied between saidfirst and second electrodes, a power supply means including a loadimpedance connecting said second and third electrodes to said powersupply, means for applying said amplified electrical signal between saidfirst and second electrodes, and adjustable bias means for biasing saidfirst electrode relative to said second electrode.
 11. In a medicalultrasonic doppler instrument as defined in claim 10, said amplifierdevice being a transistor having base, emitter and collector electrodesrespectively constituting said first, second and third electrodes. 12.In a medical ultrasonic doppler instrument as defined in claim 11, saidadjustable bias means comprising a potentiometer having end terminalscoupled to said power supply and having a movable contact coupled tosaid base electrode.
 13. In a medical ultrasonic doppler instrument asdefined in claim 1, said detector means including a product detector,and an oscillator for energizing said transmitting transducer means andfor supplying a signal to said product detector.
 14. In a medicalultrasonic doppler instrument as defined in claim 13, said productdetector comprising a field effect device having a pair of controlelectrodes, means for applying said amplified electrical signal to oneof said electrodes, and means for applying said signal from saidoscillator to the other of said electrodes.